Advice on how to make an offer for a property that ISN'T for sale

[Manish A.]

Lady has a commercial property between 2 of our empty commercially zoned lots.  Would be of high value if we could acquire hers and be able to combine all 3 lots.  From what I've heard she's in her 50s and only using the property one day a week for her business (psychologist), and has a main office elsewhere.  

Our plan is to approach her with a nice offer, maybe include free rent for a year after the sale to give her time.  

Since we want to do this right the 1st time, just wanted to get any advice of DOs and DON'Ts in a situation like this or any other helpful thoughts?

Thanks

Miz